Mode-determined unidirectional phonon transducers for minimal frequency splitter

The development of diverse fields like acousto-optics, spintronics, quantum technology raises new demand on precise phonon manipulation, while surface acoustic wave (SAW) on piezoelectric substrate is a promising platform. Besides the widely studied on-propagating manipulation issues, the emission of phonon also serves as an important design consideration in the system. In this work, through ion slicing technology, heterogeneous substrate with 42°Y cut LiTaO₃ thin film directly bonded on 4H-SiC is fabricated. The heterogeneous substrate enables double-modes natural unidirectional transducer (DMNUDT). Determined by the vibrating mode, unidirectional emission of shear horizontal SAW phonons and longitudinal leaky SAW phonons to opposite direction by symmetric transducers is realized, which is beyond the capability of previous asymmetric unidirectional transducers. Based on the fascinating phonon radiation features of DMNUDT, we propose the minimal on-chip frequency splitter, that can split mixed frequency components of AC signal into channel. The demonstrated piezoelectric frequency splitter can achieve transmission ratio of greater than 15 dB within the footprint of a resonator.